Electric heating elements are used more and more widely, and the conventional methods for temperature-power control of the electric heating elements usually utilize absolute temperature control manner, that is, these methods only sample and control the absolute temperature of the heating element, but cannot determine the work status of the heating element and the thermal requirement of the heated object and its effect to the temperature. When the temperature is falling, the transient response of the heating element is poor, thus the re-rising of the temperature is slow, and this cannot be used in the case that the heat transfer of the heating element changes rapidly. For example, temperature of the electric soldering iron is very high when it does not touch the metal to be welded, once it touches a big-size metal object or keeps contacting with the metal object for a long period of time, temperature of the electric soldering iron may fall rapidly due to the fast heat transfer, especially in the case that the metal to be welded has a large surface or the environmental temperature is low. The conventional temperature control technologies for the electric soldering iron only consider the absolute temperature of the welding head, therefore the adjusting speed is slow, the power adjust cannot catch up with the variation of temperature, and the change of the power adjustment cannot catch up with the change of the temperature, even in some particular situations, the welding requirements cannot be satisfied because of the control delay.